Ehm, we are native spanish speakers aswell, i really don't see anything wrong with the pronunciation, we consider our spanish to be pretty flawless if you ask me. I always, double, triple and quadra check everything i upload, but in the pronunciation aspect, i really dont see anything wrong, i send the song to a dozen of friends before making it public and nobody said a word about the pronunciation.
For the rest, yeah, it depends on tastes, the sliding part you pointed is a style of singing, you can hear similar sliding in Beyonce or other artists.